Eutrophication 123

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Eutrophication Jayeshkumar Nikam (07D07028)

Transcript of Eutrophication 123

Jayeshkumar Nikam (07D07028)

Definitiony Eutrophication can be defined as a process by which a

body of water like lakes, estuaries or coastal areas becomes enriched with nutrients that stimulates the growth of specific plant life usually resulting in the depletion of dissolved oxygen.

The Processy Without human intervention, Eutrophication can also

happen naturally y The lake in its early stages is called Oligotrophic. At this stage the nutrient levels in the lake are very low and the lake is colder as compared to its subsequent stages. y Natural processes such as soil erosion by wind and leaching by rain water add up the nutrients in the lake body

The Process(cont.)y The rate of input of nutrients from these sources

generally exceeds their losses from the lake and after a few years the nutrients begin to accumulate in the water body and the lake enters its next stage called Mesotrophic y As the amount of nutrients continuously increases, a stage is reached when the amount of vegetation increases so much that the dissolved oxygen in the lake is almost depleted and this old stage of lake is called Eutrophic

The Process(cont.)y The natural process of eutrophication is very slow and

it takes about decades for the lake to become eutrophic y But due to human intervention the rate at which nutrients are deposited has increased and the typical rates of silting are as high upto 1-2m/yr

Eutrophication in terrestrial ecosystemsy Accumulation of nitrogen containing compounds in

the soil leads to terrestrial eutrophication y This brings about some undesirable changes in the natural vegetation and favours the growth of some specific species over other leading to an imbalance in the ecosystem. y For example, some of the orchid species in Europe are endangered due to terrestrial eutrophication.

Eutrophication in coastal water bodiesy Eutrophication is also observed in coastal water

bodies. Coastal Eutrophication process works in the same manner as eutrophication of lakes y The World Resources Institute has identified about 375 eutrophic zones in the world concentrated in coastal areas of Western Europe, the Eastern and Southern coasts of US, the East Asia, particularly in Japan

Characteristic of Eutrophicationy According to The United States Environmental

Protection Agency (USEPA), the Eutrophication process can be characterized using the following criteria: 1) Decreasing dissolved oxygen concentration 2) Increasing nutrient concentration 3) Increasing suspended solids, especially organic materials

Characteristic of Eutrophication(cont.)4) Increasing population of blue-green and/or green algae. 5) Decreasing light penetration 6) Increasing phosphorous concentration in the sediments

Comparison of Eutrophic and Oligotrophic stagesCharacte Paramete Oligotro ristic r phicPhysicalDO concentration Suspended particles Light penetration Depth Temperature HIGH LOW HIGH HIGH COOL LOW

Eutrophi cLOW HIGH LOW LOW WARM HIGH

Chemical

Nutrient concentration in water column Nutrient concentration in sediments

LOW

HIGH

Sources of Eutrophicationy We can broadly classify the sources of eutrophication

as : 1) point sources 2) non point sources

Point Sourcesy In point sources various nutrients travel directly into

the water body from a concentrated source y Point sources are easy to control as compared to non point sources

Examples of point sourcesy Effluents from municipal and industrial waste water y Runoff from waste disposal systems like landfills y Overflows from sanitary sewers y Direct discharge of untreated sewage

Non Point Sourcesy In non point sources, the nutrients travel to the water

body from a dispersed source y It is generally a kind of runoff pollution

Examples of non point sourcesy Runoff from agriculture y Runoff from construction sites y Runoff from abandoned mines

Water Quality ParametersParameterDissolved Oxygen

SignificanceGeneral indicator of water quality and source of oxygen for respiration Clog fish gills, bury eggs, reduce light penetration, increases heat absorption Represents total mineral content which may or may not be toxic

LevelMinimum acceptable level, 2.5 mg/L; 1015mg/L for reproduction of desirable fish Dependent on location

Total Suspended Solids (TSS) Total Dissolved Solids (TDS)

A maximum of 400 mg/L for diverse fish population

Water Quality Parameters (cont.)BODAmount of dissolved oxygen removed during decomposition of organic matter in a given time; a general indicator of contamination due to biodegradable organic matter Indicates the concentration of materials oxidizable by chemical reaction Indicates the addition of acids or bases BOD - Water Status 1 mg/L - Very clean 2 mg/L Clean 3 mg/L - Fairly clean 5 mg/L Doubtful 10 mg/L Contaminated

COD

0.5 mg/L indicates very clean streams

pH

pH depends on actual system

Water Quality Parameters (contd)NitrateA major plant nutrient; in A maximum of 0.3 mg/L high-concentrations, it to prevent excessive can promote excessive fertilization of streams plant growth; major sources are fertilizers, sludge and sewage A major plant nutrient; major sources are detergents, fertilizer, sewage A maximum of 0.03 mg/L total inorganic phosphate is a common criterion

Phosphate

Factors affecting Eutrophicationy The commonest limiting nutrient in the fresh water

bodies is phosphorus and the second common being nitrogen y Hence nitrogen and phosphorus levels in water are often crucial in predicting algal blooms

Fact rs aff cti g E tr(c t )

icati

y Domestic waste water is derived from a vast number of

minor sources from domestic households and commercial premises y Typical nutrient content of human wastes

Phosphorus Nitrogen

2.18g/capita/day 10.8g/capita/day

Fact rs aff cti g E tr(c t )

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y Thus we see that sewage derives majority of its

nutrients from human excreta but phosphorus is also contributed largely by detergents y Phosphorus derived from detergents is still a major issue because alternative technologies are still in the developmental phase y Phosphorus in detergents is in the form of sodium tri polyphosphate which is readily hydrolyzed to form biologically available orthophosphate

Fact rs aff cti g E tr(c t )

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y As phosphorus removed after secondary treatment is

of the order of 50-60%, huge amounts of orthophosphates are discharged into the reservoir y Studies are currently going on to evaluate the use of sodium alumino-silicate (zeolite A) and nitrilo tri acetic acid (NTA) in place of sodium tri polyphosphate

Fact rs aff cti g E tr(c t )

icati

y Similarly the industrial waste waters contribute to the

eutrophication of lakes and reservoir by discharging organic and inorganic wastes y Food processing industries such as dairies, slaughter houses and canning plants contribute very much to the organic wastes y Inorganic wastes mainly come from textile industry, metal industry

Fact rs aff cti g E tr(c t )

icati

IndustryVegetable Processing Chemical manufacturing Iron and steel manufacturing

Factors affecting qualityBOD, suspended solids, colour BOD, ammonia, phenols, non biodegradable organics, heat Cyanide, Phenols, Thiocyanate, pH, ammonia, sulphides Cyanide, copper, cadmium, Phosphate, nickel, pH Suspended solids, pH, BOD

Metal Finishing Brewing

Fact rs aff cti g E tr(c t )

icatiBOD, pH

Dairy Products Oil refining Power generation

Heat, ammonia, pH Heat

Methods to prevent Eutrophicationy The following preventive methods are generally

adopted to prevent eutrophication: 1) Discharge Control 2) The use of Pre-Impoundments 3) Land use practices

Discharge Controly As shown in the above table, water quality parameters

are suggested by the respective pollution control boards of different countries which must be adhered to by industries and municipal bodies as a preventive measure to avoid eutrophication

The use of Pre-Impoundmentsy In this method, impoundments are constructed at

points where the influent stream enters the lake or reservoir y This acts as a settling tank and reduces the phosphorus discharge in the lake y The settling efficiency of this kind of impoundment depends mainly on the retention time y These impoundments must be maintained in aerobic conditions and also must be regularly dredged so as to prevent themselves getting eutrophic

Land use practicesy Strict control measures must be imposed on

agriculture and industry y Terracing and contour farming must be practiced to reduce runoff and erosion y Proper measures should also be taken to reduce urban runoff quality

Methods to cure Eutrophicationy The following methods were used quite successfully in

some cases to cure already eutrophic lakes: 1) Diversion 2) Dilution

Diversiony This technique diverts the nutrient rich water and thus

prevents it from entering the water body y Such a diversion may seem to be diversion of the problem but the wastewater can be thoughtfully diverted for agricultural irrigation y This practice was hugely followed in U.S.A. and has also helped in the recovery of many lakes including the Lake Washington

Diversion (cont.)y In 1955, the lake was receiving 24,000 cubic meters of

effluent per day from 10 different sewage treatment plants in its area y The total diversion of these waters into salt water inlet of the pacific ocean has allowed almost complete recovery

Dilutiony Dilution has always been a method to reduce the

concentration of pollutant and thus reduce its effect y Thus the dilution of eutrophic waters with treated water will reduce its nutrient concentration and hence will reduce the nutrient uptake by biomass and thus its growth y The amount of treated water added also affects the residence time of various nutrients

Dilution (cont.)y This method was successfully implemented in various

lakes y For example, in Green Lake in Seattle U.S., treated water was added to the eutrophic lake which decreased the residence time of the nutrients to about 4 months resulting in a rapid alteration to the mesotrophic state y Turbidity decreased and even the chlorophyll A concentration decreased.

Eutrophication in the Swan Reservoiry Swan river is located around Perth in WesternAustralia. y The typical climate of wet winters and hot dry summers over here supports algae blooms. y Also the sandy soils which have poor nutrient holding capacity, the strongly seasonal water flow and the seasonally changing salinity conditions make it even more susceptible to eutrophication

Eutrophication in the Swan Reservoir (cont.)y By mid winter, the swan catchment gets saturated by

rainfall and the runoff flows into the river y During spring, the catchment dries out and the freshwater flows into the estuary becomes negligible which allows the seawater to flow upstream from the Indian Ocean. y This wet-dry cycle allows the estuary to oscillate from freshwater conditions in winter to saline conditions in summer which is very favorable for algal blooms.

History of Swan Reservoiry Early human settlement cleared land for agriculture

which led leaching of fertilizers into the waterways. Also the urban and industrial development in and around Perth dumped sewage and industrial waste which led to drastic increase in the levels of N & P. y These changes led to poor water quality in the SwanCanning system, especially between the 1920s and 1970s, and produced smelly heaps of decaying macro algae on the river s beaches and foreshores.

History of Swan Reservoir (cont.)y Government policy since the 1930s, and

particularly between the 1950s and 1970s, encouraged the relocation of industry and sewage treatment away from the metropolitan area. This effectively eliminated large point sources of nutrients and industrial waste and significantly improved water quality in the lower and middle estuary.

Current situationy Current water quality problems in the Swan reservoir

is due to non point sources. y The non point sources are difficult to identify, control and manage. y The algae that now cause problems are not seaweeds or macro algae, as was the case in the past, but microscopic phytoplankton (microalgae).

Control and Managementy An Action Plan was released as part of Swan Cleanup

Program by Swan River Trust. y The Action Plan stressed the reduction of nitrogen and phosphorous release in the estuary to lower the frequency and duration of algal blooms that occur. y The Action Plan aims to reduce nutrient inputs from rural and urban runoff and ground water flows e.g. from fertilizers applied to lawns and gardens, and also aims to prevent erosion and degradation of foreshores.

Control and Management (cont.)y It also emphasizes control and better management of

high nutrient generating land-uses e.g. piggeries, intensive horticulture, sports grounds, runoff from light industrial areas, etc. and better management of leaching of nutrients and other pollutants from land fill sites.

Referencesy Wikipedia y Eutrophication and algal blooms in inland reservoirs, y y y y

AKM M Rahman & Dhia Al Bakri CPCB website Decaying lakes, B Henderson Sellers & H. R. Markland An assessment of eutrophication in Australian inland waters, J. I. Skiko River Science Issue 03